OBJECTIVE: This study aimed to evaluate the impact of preoperative haemoglobin levels on early morbidity and mortality in patients undergoing isolated aortic valve replacement. MATERIAL AND METHODS: This retrospective study included 149 patients who underwent aortic valve replacement at Akdeniz University between 2013 and 2023. Patients were categorised as anaemic or non-anaemic based on the World Health Organisation (WHO) definition. Preoperative characteristics, intraoperative parameters, and postoperative outcomes were compared. Statistical analyses were performed using SPSS 27.0, with significance set at p < 0.05. RESULTS: Anaemic patients were significantly older (62.8 ± 12.7 vs. 56.3 ± 18.3 years, p = 0.011) and had lower body surface area (1.84 ± 0.20 vs. 1.92 ± 0.24m2, p = 0.026). Aortic root diameter was smaller in the anaemic group (29.2 ± 3.7 mm vs. 31.2 ± 3.9 mm, p = 0.001). Prior cardiac surgery was more common in anaemic patients (23.1% vs. 9.1%, p = 0.025). Intraoperative blood transfusion (p < 0.001) and extubation time (p < 0.001) were significantly higher in anaemic patients. Postoperatively, renal failure (p = 0.010) and sepsis (p = 0.030) were more frequent. In-hospital mortality was higher in anaemic patients (10.3% vs. 1.4%), and this difference was statistically significant (p = 0.024). ICU length of stay was found to be significantly longer in anaemic patients (6.1 ± 10.9 days vs. 3.5 ± 2.1 days, p = 0.005). CONCLUSION: Preoperative anaemia was associated with increased postoperative morbidity and in-hospital mortality. Haemoglobin level emerged as an independent predictor of mortality, underscoring the importance of preoperative haemoglobin optimisation to improve surgical outcomes.